Chrysler Repair: Air distribution from heater/AC not adjustable: 90, vacuum gauge, brake master cylinder

Question
My 1990 New Yorker AC Air Blows in the Floor Vents, Not through the front Vents, Why?

Answer
Hi Warren,
The doors inside the HVAC unit under the dash are operated by vacuum that is drawn from the intake manifold of the engine when it is running. If you look near the power booster canister for the power brakes (just above the brake master cylinder under the hood) you will see a large rubber hose that comes from the engine to the booster cannister. At the connection of the two there is a thin plastic hose that branches off and is routed to and thru the firewall about midline of the body well below the windshield. That hose is the vacuum hose that is attached on the other side of the firewall to a vacuum splitter switch which connects the vacuum to various door actuators depending upon how you have the air distribution selected. The most common reason for a loss of control over the air distribution is that the vacuum hose has disconnected from the nipple where it splits off the large rubber hose. So find the plastic hose and make sure that it is connected firmly. Then inspect it for cracks along the way to the firewall. If you do that and you still don't get air distribution as selected when the engine is running then there may be a crack in the line on the otherside of the firewall. There also is a small check valve in the line so look closely at the hose at that valve.
If that doesn't solve the problem then the vacuum splitter will have to be inspected. Ideally you should have a vacuum gauge to do that. So verify that you can feel some suction on the line inside the cabin with the engine running by putting the tip of your finger over the end of the line when you disconnect it from the check valve or the splitter.
Most likely though you will find that it simply isn't connected to the nipple where is splits off.
Roland